Morphology Evolution Induced by Sequential Annealing Enabling Enhanced Efficiency in All-Small Molecule Solar Cells

Advances in small-molecule non-fullerene acceptors have led to increase in power conversion efficiencies (PCEs) of organic solar cells. Simultaneously, small molecules feature lower viscosity and better crystallization properties, which makes it easier to manipulate the molecular packing, film morphology, and device performance during the fabrication process. In this contribution, we fabricate all-small molecule solar cells based on BTR:Y6 with sequential annealing, and an enhanced PCE of 11.88% is achieved with JSC of 22.60 mA cm–2, VOC of 0.837 V, and FF of 62.79%. The morphological study reveals the concomitant of third-order lamellar and π-π stacking peaks and the improved BTR crystallite, indicating the improved crystallization properties. At the same time, the favorable film morphology with an interpenetrated network structure is also formed in blend films with sequential annealing. Thus, bimolecular and trap-assisted recombination can be effectively suppressed in the optimal solar cell devices. Such studies underline the significance of morphology control in fabricating highly efficient small-molecule solar cells.